Nowadays, more and more flat lighting devices are adopting a plurality of light emitting diodes (LEDs) as a light source in place of the traditional incandescent lamps or fluorescent lamps. When being used as a light source in such a flat lighting device, the LEDs are typically disposed directly at the bottom of the flat lighting device. The LEDs emit light rays, and the light rays have the maximum intensity in a normal viewing direction (i.e., in a direction perpendicular to light emitting surfaces of the LEDs). Therefore, the light rays from the flat lighting device are non-uniform, and a local dark spot (i.e., an area having the minimum light intensity) or a local bright spot (i.e., an area having the maximum light intensity) can be seen.
To eliminate the local dark spot or local bright spot described above, a light diffuser plate may be disposed in front of and spaced apart from the LEDs. However, this increases the overall thickness of the flat lighting device. Another approach to eliminate the local dark spot or local bright spot is to increase the number of LEDs. However, this adds to the manufacturing cost of the flat lighting device.
Accordingly, an urgent need exists in the art to overcome at least one of the aforesaid shortcomings